1. Field of the Invention
The present invention relates to PCR apparatus. More particularly, the present invention relates to vessels, containers, kits, assemblies, and methods for effectively conducting PCR on samples.
2. Description of the Related Art
Biological testing has become an important tool in detecting and monitoring diseases. In the biological testing field, thermal cycling is often used to amplify nucleic acids by performing polymerase chain reactions (PCR), for example, and other reactions. PCR typically is carried out in containers such as tubes, plates, or trays having multiple wells. In such containers, reagents such as DNA polymerase, nucleotides, oligonucleotide primers, buffers, and a DNA template are exposed to thermal cycling to promote amplification of the DNA template. See also U.S. Pat. Nos. 6,015,534; 5,710,381.
The wells in PCR plates typically are sealed during the PCR cycling to minimize volume loss and contamination of material contained within. Heat-sealed blankets, adhesive blankets, caps, or other such means are often used to seal the wells in the PCR plates. For example, U.S. Pat. Nos. 5,721,136 and 6,127,188 propose materials that control the level of sample loss during chemical reactions. Additional filter material may be used to process samples within the PCR plate wells. For example, commonly assigned U.S. Pat. No. 6,159,368, the entire disclosure of which is incorporated by reference herein, describes, among other things, a multi-well micro-filtration apparatus that provides for the separate processing of filtrate from at least one well of a multi-well micro-filtration device.
Because of the relatively thin layer of adhesive on an adhesive blanket, for example, and the pressure generated within the wells, a compliant pad typically is placed between the blanket and a cover to assure a robust seal between the blanket and the individual wells within the tray. These compliant pads are typically pads that are flexible and assume the shape of the material they are pressed against. The compliant pad may be a silicone or foam pad cut to fit on top of the PCR plate.
Thermal cyclers, such as those described in U.S. Pat. Nos. 5,475,610 and 5,602,756, both incorporated by reference herein in their entirety, are typically used to amplify nucleic acid templates by PCR. With the introduction of direct-reading optical PCR systems, such as the 5700, 7700, and 7900HT systems from Applied Biosystems of Foster City, Calif., holes were added to the compliant pads allowing real time visual access by the optical system to the samples in the wells through the optically clear blanket. See also U.S. Pat. No. 5,928,907 and 6,015,674, both incorporated by reference herein in their entireties.
Real time visual monitoring of samples typically is practical with 96 well plates. Generally, with higher density plates having increased numbers of wells, the typically higher tolerance build-up between the plate and dimensionally unstable compliant pads may present a need for addressing the increased tolerance.
Furthermore, typical compliant pads may not always be acceptable for manual or robotic handling. Compliant pads could be inadvertently picked up by a robotic mechanism by the upper tray in the stacker and get lodged between the PCR plate and the thermal cycling block. Further, a die-cut compliant pad could move, causing partial or complete blockage of the optical path.
Additionally, heat sealed sheet-covered PCR plates typically could become warped because of the shrinkage of the heat sealed covers and plates, making them difficult or impossible to pick up with standard robotic mechanisms, particularly if used with heat-sealed covers or after thermal cycling.
Die-cut adhesive compliant covers also could be difficult to align and were not suitable for reuse. These covers could allow a robot grip inadvertently to pick up two trays at the same time by clinging to the bottom surface of the upper tray in a stacker.
There exists a need for a high tolerance rigid cover that is easily installed, economical, and maintains the fit of the PCR plate to enhance proper robotic handling, such as stacking and handling, and preserving the sample contained within. Additionally, the rigid cover should be able to withstand the conditions associated with thermal cycling, such as the heat, without unacceptable deforming, warping, or buckling. The rigid cover should also not act as a heat sink, thereby decreasing the efficiency of the thermal cycling process. Finally, the rigid cover should be chemically compatible with any samples and reagents used in the process and should not affect their chemical reactions.
The advantages and purpose of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purpose of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention is directed to a cover for retaining a sealing sheet on a surface of a PCR plate having sample wells depending from and opening through the surface, and a peripheral wall surrounding the sample wells and connected to a base. The cover includes a substantially rigid sheet capable of maintaining the surface of the PCR plate in a pre-thermal-cycling shape during a PCR thermal cycling process, and a resiliently compliable sheet cooperable with one side of the substantially rigid sheet to press the sealing sheet against the surface of the PCR plate to maintain a seal in the wells. At least one retaining device is attached to the substantially rigid sheet to be engagable with the PCR plate to retain the substantially rigid sheet and the resiliently compliable sheet in a condition to press the sealing sheet a against the surface of the PCR plate. The retaining device may be embodied in various forms and multiple retaining devices may be used
In another aspect, the advantages and purpose of the invention are realized and attained by an assembly for processing samples in PCR, including a PCR plate having sample wells depending from and opening through a surface in the plate, and a peripheral wall surrounding the sample wells and connected to a base, and a cover for the PCR plate. The cover includes a substantially rigid sheet capable of maintaining the surface of the PCR plate in a pre-thermal-cycling shape during a PCR thermal cycling process and a resiliently compliable sheet cooperating with one side of the substantially rigid sheet and capable of pressing a sealing sheet against the surface of the PCR plate to maintain a seal in the wells. At least one retaining device is attached to the substantially rigid sheet and engagable with the PCR plate to retain the substantially rigid sheet and the resiliently compliable sheet in a condition to press the sealing sheet against the surface of the PCR plate.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the apparatus, assemblies, kits, and methods particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.